Preterm birth (PTB) is the number one cause of infant mortality and morbidity. Amniotic fluid (AF) infections are prevalent in PTB. One hypothesis to explain this is that the organisms originate from the vagina and ascend into the uterus. However, some organisms from AF appear to be of oral origin. One of the most frequently isolated species from AF, Fusobacterium nucleatum, is highly prevalent in periododontal plaques and infections. F. nucleatum is capable of invading human gingival epithelial and umbilical cord vein endothelial cells. Preliminary studies revealed that haematogenous infection of. F nucleatum induced pregnancy complications in mice. Therefore, it is reasonable to speculate that the hematogenous route of transmission may also occur in humans. To test this possibility, we aim to investigate the source of the F. nucleatum infection in AF. AF samples will be collected via amniocentesis from 400 patients in preterm labor with intact fetal membranes at a gestational age of < 32 weeks. Vaginal, blood, and subgingival plaque samples from these patients will also be collected. AF infections by all bacteria and by F. nucleatum, along with the control urogenital species, Ureaplasma urealyticum, will be examined by polymerase chain reactions (PCR) using primers specific for the conserved and hypervariable regions of 16S ribosomal RNA, respectively. Once F.nucleatum is identified in AF, the vaginal, blood, and plaque samples of the same patient will be examined by PCR. in addition, since F. nucleatum is highly heterogeneous, in order to clearly identify the source of infection, F. nucleatum will be isolated and identified to the subspecies level and differentiated by DNA fingerprinting. The results from this pilot study will enable subsequent investigation into the mechanism of infection, identifying virulent strains of AF-associated F. nucleatum for diagnostic purposes, and intervention studies aimed at reducing the incidence of preterm birth. [unreadable] [unreadable]